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Rash of Browntail Moths Making Life Painfully Itchy for Mainers

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A photo provided by the Maine Forest Service, browntail caterpillars in the fall get their web ready for winter, in Bath, Maine .Browntail moth caterpillars are on the rise in Maine. The caterpillars’ hairs can cause a painful rash in humans. State scientists say it’s difficult to control the spread of the bugs, which has been aided by dry weather. (Maine Forest Servic ACFvia AP)

A species of moth that is infamous for an itchy, painful rash caused by the hairs of its larvae increased in population and territory in Maine this year and will likely spread even more in 2017.

The browntail moth is an invasive insect that came to New England from Europe just before the turn of the 20th century. They produce caterpillars that have poisonous hairs that can cause a skin inflammation in humans that resembles a poison ivy rash.

The leaf-eating caterpillars have defoliated 63,000 acres of trees this fall, more than six times the acreage of last fall, underscoring their expansion, Maine forest entomologist Charlene Donahue said. She said the moths have spread across a much wider landscape this year and will likely be worse next year when new larvae hatch.

Dry weather may have allowed the caterpillars to thrive, as they are susceptible to a fungus that is more likely to afflict them in wet weather, Donahue said. The moths' range in the state also spread this year; they were mostly found in coastal Sagadahoc and Cumberland counties, but some were found as far north as Millinocket, in northern inland Maine, she said.

"The potential for them to be much wider spread is there," Donahue said. "In the areas affected, they were really bad, and certainly affected people's quality of life."

Browntail moths spread all over New England by the 1910s, but populations declined to just Maine and Cape Cod, Massachusetts, after several decades. They can be controlled with pesticides and destroying the webs that contain colonies of larvae.

Decades ago, the state sought to control the population of the moths with parasitic flies and wasps that eat them. These days, Maine is suggesting residents take steps to mitigate the moths spread, such as clipping down the webs and burning them or soaking them in soapy water, Donahue said. Professional pesticide applicators can also be called on to spray them when they nest in treetops, she said.

Donahue said the threat of the caterpillars' hairs can also be reduced by wearing protective clothing, mowing the grass when it's wet and avoiding hanging laundry outside. The caterpillars' hairs can also cause respiratory problems in people.

The moths remain an occasional problem on Cape Cod, where Cape Cod National Seashore employees occasionally complain of contracting the rashes. But that's the only place in Massachusetts where they're a problem, said Joe Elkinton, professor of entomology at the University of Massachusetts.

Surprisingly, the moths are not such a problem on the New Hampshire coast as they are on the Maine coast. Kyle Lombard, forest health specialist with the New Hampshire Division of Forests and Lands, said the state has no issues with browntail moths, and he's not sure why. They also haven't been seen in Vermont in nearly a century.